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Flap Issue Take 2...

ViperDriver

ViperDriver

Member
Howdy,

Yesterday in hour 33 of phase one on our 7A, I had the inboard third of the right flap pop over the wing skin and do some damage. I was running the flaps to full up for takeoff when the 'pop-crunch' was heard. Slid the canopy back to take a look and confirm. Flaps were then lowered and they popped back into the proper position but left the wing skin bent and deformed, see pics. The flaps were part of the QB kit so I am pretty sure they are to spec. I am also confident that the install was correct (rechecked this with the plans and some trusted builders after the incident yesterday). The temp was extremely cold yesterday, 15 degrees and I had taxied with the flaps in the full down position. We are going to adjust the flap push rod and recheck everything another ten times after the wing is repaired.

Has this happened to anyone? What else can contribute to this?

I'm pretty sure the push rod fix will do it but wanted opinion just the same.



(Attempted this post yesterday but it seemed not to be working, new to posting on here. If an admin can mort out that other post that would be great. THANKS TO flyinmonque for your help. :cool:)



wing skin deformed where flap came out

 
Thanks Ill be better about searching! :cool: Sorry for posting something that has been hit already but on that note I hope everyone looks at the pics and thinks about it so they can avoid having this happen. Just went through all that posts in the links and got quite an education on both the problem and what can be done thanks. I guess this is a common thing.
 
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Doubtful, Jim.........

.......since the -9's fowler flaps are hinged differently than the 6,7,8. They're hinged by a long piano hinge and the upper surface is real close, sometimes touching the trailing edge of the upper skin and barely tucked under. A little extra travel and the flap leading edge jumps up, interfering with the top skin as they retract.

Regards,
 
rv9aviator said:
Is this problem only on the 6-7-8 models or can it also happen to a 9.

Thanks
Click to expand...

pierre smith said:
.......since the -9's fowler flaps are hinged differently than the 6,7,8. They're hinged by a long piano hinge and the upper surface is real close, sometimes touching the trailing edge of the upper skin and barely tucked under. A little extra travel and the flap leading edge jumps up, interfering with the top skin as they retract.

Regards,
Click to expand...

Jim,

In addition to what Pierre said, the skin on the forward edge of the -9's flaps are riveted to the spar top and bottom. On the -6 & -7 (I don't know about the -8) the bottom of the leading edge on their flaps is not secured, just bent into position.

See this picture from Dan C's web site:
20020829_left_flap_done.jpg
 
I feel better now. I'll check the operation anyway but looks like the 9 is made substantially different than the others.
Thanks
 
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What's In The Actuator?

I curled the right outboard top skin and tweaked the flap leading edge a week ago. First clue was the plane not flying straight or as fast. Reading other posts, I think my bumping the fully extended flap while loading set up the problem. Ex post facto, it takes a whole lot of force to pop the flap leading edge to where it will bind.

I read where others have set the travel to less than the usual 45degrees the drive screw allows when built to plans (RV-7). My concern is not allowing the full range means the up stop becomes the flap skin overlap with the fuse. (During construction, the pushrod attachment to the flap could be moved further away from the hinge to reduce motion, but that's not possible now.) I asked Van's about how the internal clutch works, could it be adjusted, how strong is it, etc.; they didn't know. Recommendation was install limit switches.

So my question for those of you who let the flap/fuse overlap limit up travel rather than the clutch in the drive mechanism, what's been the effect on the flap skin, and how repeatable is the up limit?

John Siebold
 
I would never use the flap skin as a stop for the up travel. Doing so stalls the motor each time you put the flaps up and could damage the motor or kill the screw/nut inside the linear actuator. You might also pull the threads out of the pushrod tubes.

If your going to do anything, put in a down limit switch to kill the power early before the linear actuator decouples at the end of the stroke.
 
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Right you are, Brian

Brantel said:
I would never use the flap skin as a stop for the up travel. Doing so stalls the motor each time you put the flaps up and could damage the motor or kill the screw/nut inside the linear actuator. You might also pull the threads out of the pushrod tubes.
Click to expand...

... or you might even bend your flaps and/or fuselage. That actuator has a lot of torque... Anyway, something's gonna give.

Brantel said:
If your going to do anything, put in a down limit switch to kill the power early before the linear actuator decouples at the end of the stroke.
Click to expand...

Exactly. Section 15 of the builder's manual specifies a maximum down travel on the flaps of between 40 and 45 degrees. Set it to 40 degrees using a limit switch and you're good to go.
 
As Mel would say here about now, manual flaps will let you know when things arn't right.
 
Manual vs. electric is not the issue

gasman said:
As Mel would say here about now, manual flaps will let you know when things arn't right.
Click to expand...

Every engineering decision is a compromise, a trade-off between one set of problems and another. But the problem we're talking about here -- the flap skin popping over the wing skin due to excessive flap travel -- is not unique to electrically actuated flaps. Either way, electric or manual, you'd have to limit the travel somehow to prevent this problem.

In the case of manual flaps, the problem is easily solved with a mechanical stop to set the down travel limit. In the case of electric flaps, the problem is easily solved with a limit switch to set the down travel limit. Different design, so different solution. But both are cheap and simple and effective in solving this problem. Electric vs. manual actuation is not really the issue here.
 
roee said:
Every engineering decision is a compromise, a trade-off between one set of problems and another. But the problem we're talking about here -- the flap skin popping over the wing skin due to excessive flap travel -- is not unique to electrically actuated flaps. Either way, electric or manual, you'd have to limit the travel somehow to prevent this problem.

In the case of manual flaps, the problem is easily solved with a mechanical stop to set the down travel limit. In the case of electric flaps, the problem is easily solved with a limit switch to set the down travel limit. Different design, so different solution. But both are cheap and simple and effective in solving this problem. Electric vs. manual actuation is not really the issue here.
Click to expand...

I think you miss the point. Gasman means that the feedback of the manual flaps keeps you from bending the metal.

Hans
 
Limit Switches?

Shouldn't you be able to adjust for proper flap travel with Rod End adjustments at the Flap Actuator and Flap Pushrods and/or reworking the Pushrod length?
The Actuator travel is fixed but can't you shorten or lengthen its affect with those adjustments to certain limits anyway?
 
Not unless you allow the system to come up against a hard stop (not recommened) or you change the pivot points (hard to do).

The travel to free wheeling on the flap motor is fixed in both retract and extension so the only way to change the travel of the flaps is to change the geometry of the linkage or stop the motor (electrically or by binding it against a hard stop) before it reaches the free wheel point.
 
Hmmm....

Brantel said:
Not unless you allow the system to come up against a hard stop (not recommened) or you change the pivot points (hard to do).

The travel to free wheeling on the flap motor is fixed in both retract and extension so the only way to change the travel of the flaps is to change the geometry of the linkage or stop the motor (electrically or by binding it against a hard stop) before it reaches the free wheel point.
Click to expand...

The Flap Actuator and the Flap Rod do change in geometry a bit based on length. The Actuator is hinged at the top allowing it to move away from the Flap Actuator housing a couple of inches or more, like an elbow, to follow the path of the weldment. The Flap Rod moves fore and aft about an inch or more.
So, hinge lines are not all lined up. If we change the length of either of these, we have to be changing something in the geometry. Just not sure adjustments to the length of the Actuator or Flap Rod would have enough affect to help folks with this problem.
I could be all wet on this.
 
These arcs are so slight, not much to be gained by this since you are very limited in how much you can change the lengths of the actuator and the pushrods.
 
up vs. down limit switch

Brantel said:
If your going to do anything, put in a down limit switch to kill the power early before the linear actuator decouples at the end of the stroke.
Click to expand...

Just to point out: some (most?) folks prefer to have an up limit switch, if you're only going to have one.

Search the site for "flap limit switch" if interested in examples.

--Paul
 
It really doesn't matter unless your wanting to have a maintained up toggle switch so you can flip it to up and forget the flaps. In that case you would need the limit on the up stopping position.
 
An ounce of prevention vs. a pound of cure

nucleus said:
I think you miss the point. Gasman means that the feedback of the manual flaps keeps you from bending the metal.

Hans
Click to expand...

Hans & Gasman, I got your point. You're saying that you'd feel through the flap handle that you're about to bend metal, so you'd stop retracting the flaps. Then you could pop the skins back in place, hopefully still unbent, when you're on the ground... I get it, I just think it's the wrong approach to the problem.

I don't think you really need feedback telling you that this failure mode has already occurred (that the flap skin has popped over the wing skin, whether it's been bent yet or not). What you do need is to build in a simple safeguard to ensure that this failure mode simply cannot occur in the first place. I think that's the right approach. And incidentally, that can be accomplished easily with either manual or electric flaps. That was the point I was trying to make.
 
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